Re: [PATCH 2/2] i2c: i2c-omap: Call request_irq with IRQF_DISABLED

["Kauppi Ari (EXT-Ixonos/Oulu)" <ext-ari.kauppi@nokia.com>]

On Thu, 2009-03-12 at 01:04 +0100, ext Paul Walmsley wrote:
Hi Paul,

> On Wed, 11 Mar 2009, Paul Walmsley wrote:
> 
> > > On Fri, Mar 06, 2009 at 03:34:54PM +0200, Ari Kauppi wrote:
> > > > I have observed some Spurious IRQ's for I2C1 when all kernel hacking options
> > > > (and thus LOCKDEP) are disabled.
> > 
> > Ari, are you seeing "Spurious irq XX: XXXXXXXX, please flush posted write 
> > for irq" messages?  If so, the correct fix for this is to read from the 
> > device interrupt status register immediately after writing to it.  This 
> > forces the ARM to wait until the write to the device is complete.  Ari, 
> > could you make this change to i2c-omap.c:omap_i2c_isr() instead, and test 
> > whether this fixes the problem?
> > 
> > + u32 tmp;
> > 
> > ...
> > 
> >   omap_i2c_write_reg(dev, OMAP_I2C_STAT_REG, stat);
> > + tmp = omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG); /* OCP barrier */
> 
> You'll also want to make a similar change in omap_i2c_ack_stat(), to add a 
> read immediately after that write.

I was seeing some Spurious irq's for the I2C1 (IRQ 56).

I'm aware of flushing posted write and the very first thing I tried was
to use read-after-write for OMAP_I2C_STAT_REG (in all applicable
places). However, it didn't make any difference.

Applying Richard Woodruff's patch (mentioned earlier in thread) that
disables dev->b_hw hack for 3430 (STT/STP bits written together) and
double clears ARDY fixed the spurious IRQ issues for I2C1.

However, with the STT/STP+ARDY patch I was seeing Spurious interrupts
all over the place and the IRQF_DISABLED in i2c-omap seemed to tame them
quite well. I do agree that my approach might not be the proper one in
long term.

Best regards,

--
Ari